refactor: add explicit this-> where possible

I have knowingly skipped some files/portions of files where this would
create merge conflicts for other open PRs.

src/messages/search/AuthorPredicate.cpp

@@ -17,8 +17,8 @@ AuthorPredicate::AuthorPredicate(const QString &authors, bool negate)
 
 bool AuthorPredicate::appliesToImpl(const Message &message)
 {
-    return authors_.contains(message.displayName, Qt::CaseInsensitive) ||
-           authors_.contains(message.loginName, Qt::CaseInsensitive);
+    return this->authors_.contains(message.displayName, Qt::CaseInsensitive) ||
+           this->authors_.contains(message.loginName, Qt::CaseInsensitive);
 }
 
 }  // namespace chatterino

src/messages/search/BadgePredicate.cpp

@@ -35,7 +35,7 @@ bool BadgePredicate::appliesToImpl(const Message &message)
 {
     for (const Badge &badge : message.badges)
     {
-        if (badges_.contains(badge.key_, Qt::CaseInsensitive))
+        if (this->badges_.contains(badge.key_, Qt::CaseInsensitive))
         {
             return true;
         }

src/messages/search/ChannelPredicate.cpp

@@ -17,7 +17,7 @@ ChannelPredicate::ChannelPredicate(const QString &channels, bool negate)
 
 bool ChannelPredicate::appliesToImpl(const Message &message)
 {
-    return channels_.contains(message.channelName, Qt::CaseInsensitive);
+    return this->channels_.contains(message.channelName, Qt::CaseInsensitive);
 }
 
 }  // namespace chatterino

src/messages/search/MessageFlagsPredicate.cpp

@@ -71,10 +71,10 @@ bool MessageFlagsPredicate::appliesToImpl(const Message &message)
     if (this->flags_.has(MessageFlag::System) &&
         !this->flags_.has(MessageFlag::Timeout))
     {
-        return message.flags.hasAny(flags_) &&
+        return message.flags.hasAny(this->flags_) &&
                !message.flags.has(MessageFlag::Timeout);
     }
-    return message.flags.hasAny(flags_);
+    return message.flags.hasAny(this->flags_);
 }
 
 }  // namespace chatterino

src/messages/search/RegexPredicate.cpp

@@ -12,12 +12,12 @@ RegexPredicate::RegexPredicate(const QString &regex, bool negate)
 
 bool RegexPredicate::appliesToImpl(const Message &message)
 {
-    if (!regex_.isValid())
+    if (!this->regex_.isValid())
     {
         return false;
     }
 
-    QRegularExpressionMatch match = regex_.match(message.messageText);
+    QRegularExpressionMatch match = this->regex_.match(message.messageText);
 
     return match.hasMatch();
 }

src/messages/search/SubtierPredicate.cpp

@@ -24,7 +24,7 @@ bool SubtierPredicate::appliesToImpl(const Message &message)
             const auto &subTier =
                 badge.value_.length() > 3 ? badge.value_.at(0) : '1';
 
-            return subtiers_.contains(subTier);
+            return this->subtiers_.contains(subTier);
         }
     }